The present invention relates to a plastic intake pipe and a method of producing the same for use in vehicles such as automobiles.
In general, an intake pipe connected to a downstream side of a throttle valve is composed of an intake duct portion, an intake chamber portion and an intake manifold portion.
Heretofore, these components and parts are divisionally formed, and associated integrally in later steps. In case of a plastic intake pipe, portions of the intake pipe which are not required for high strengths, are formed by blow molding, thick portions such as flanges, are partially formed by injection-molding, and the blow-molded portion is fusion-connected to the injection-molded portion in a later step. An intake manifold portion having relatively many bent parts is formed by using a low melting point metal material such as a bismuth alloy as a core, and the core is melted and then drawn out after the intake manifold portion is injection-molded.
As explained above, an arbitrary shape can be obtained by the blow molding, but since the flange or a bracket to be externally mounted cannot be formed integrally by the blow molding, there is a problem in fixing means when the body is externally mounted. In case where a flange or a bracket is fusion-connected to the blow-molded portion later, it is necessary to widely obtain its fusion-connected surface by considering reliability for a strength of the fusion-connected part thereby to cause an unnecessary space to be increased.
On the other hand, if a low melting point alloy is used as a core likewise a molding of an intake manifold portion, a flange or a bracket may be formed integrally, but since the low melting point alloy is expensive, it introduces an increase in its cost. Further, since it additionally needs a facility for molding the core, its facility cost is not only increased, but also it causes its productivity to be remarkably decreased.
In order to solve such a problem, techniques for first forming an inside pipe by blow molding and then injection-molding an outside pipe on the outer periphery of the inside pipe with the inside pipe used as a core have been disclosed, for example, in Japanese Patent Application laid-open Nos. 63-111031 and 63-141713 official gazettes.
Since it is apprehended that the blow-molded component likewise the inside pipe used as a core in this prior art as explained above is deformed by a molding pressure in a mold in case of an injection-molding, a noncompressive material (such as sand, glass beads, liquid likewise water) must be filled in the blow-molded component.
However, a great deal of labor is required for works of sealing the noncompressive material in the blow-molded component, its operation is not only complicated, but also the noncompressive material must be heated and drawn out after the injection-molding is completed thereby to cause the working steps to be increased.
Further, when the noncompressive material is filled in the blow-molded component, the weight of the component is increased, and it becomes difficult to hold and fix the material at an accurate position in case of inserting the material in an injection mold. Accordingly, it is difficult to mold an entire intake system integrally at a downstream side of a throttle valve. As disclosed in the prior art explained above, it cannot be realized only by partially molding the intake duct portion or the intake manifold portion, but a work of connecting the components and parts is additionally required to cause the number of steps for connecting the components and parts to be increased. Moreover, a guarantee for the strengths of the connecting portions of the components and parts must be sufficiently considered.
There is another problem that the afore-described blow-molded components have a low rigidity. When the intake pipe body having the blow-molded component as the inside pipe is assembled in an intake system of an internal combustion engine, the inside pipe is elastically deformed by pressure fluctuation of the intake air which flows in the intake pipe to induce a surface vibration and thereby to cause noise to be increased.